1. Technical Field
This disclosure relates to methods and apparatus for processing and analyzing a microscopic sample, in particular, methods and apparatus for such processing and analyzing inside a charged-particle instrument such as a focused ion-beam microscope (FIB) or scanning electron microscope (SEM).
2. Background
FIB processes for lamella creation for transmission electron microscope (TEM) sample preparation have long been used in the semiconductor industry, including the use of nanomanipulators for FIB in situ lift-out (INLO) sample preparation, where the sample is lifted from some substrate, such as a semiconductor wafer. In addition to thin lamella, INLO samples have been adapted to other types of geometries such as wedges and micropillars, and they have been adapted to INLO-TEM types of in situ specimen analysis performed directly within the chamber of the charged-particle microscope. Examples of these analysis types include STEM, EDS, and EBSD, to name a few. The traditional INLO sample preparation is comprised of three main steps: 1) by induced-beam CVD deposition, glue, static, or other attachment means, attaching a nanomanipulator end-effector such as a fine probe tip to the sample destined for analysis, 2) while attached and supported by the end-effector, lifting the sample out or away from its original position, and 3) attaching the lifted sample to a new substrate or holder, such as a TEM grid, for completion of processing such as sample shaping by the ion beam or for inspection by various analytical means (such as the previously mentioned STEM, EDS, EBSD, or TEM analysis), performed either in situ or ex situ to the original charged-particle microscope chamber.
There are three primary reasons INLO samples are attached to a secondary support prior to further processing and analysis. First, this provides a means to easily manipulate a sample into different orientations to achieve the desired processing or analysis result based on using the degrees of freedom of the charged-particle beam microscope stage. Second, by placing the sample on a support directly connected to the microscope stage, additional drift or vibration effects outside those of the stage can be avoided. Third, the secondary holder or support provides an easy way to handle the sample for storage or when transferring the sample between different instruments.
The imaging requirements of charged-particle beam instruments are demanding, especially when imaging at the upper resolution limits in the range of angstroms to a few nm. Even the smallest vibration or drift can interfere with processing and analysis. In some cases, to achieve the desired performance, every unnecessary accessory on a charged-particle beam microscope is removed, as each accessory adds its own amount of drift and vibration to the entire chamber. Nanomanipulators, being accessories to these charged-particle beam instruments, have their own characteristic drift and vibration. These disturbances must be minimized to achieve the desired results if the processing and analysis are to occur while the sample is held by the end-effector of the nanomanipulator.
In practice, the sample is placed on a secondary support after the orientation steps are completed to provide stability against drift and vibration during processing, imaging and analysis. The lack of a solution to perform processing and analysis while on the end-effector means valuable instrument time is consumed with the third INLO step of attaching the lifted sample to a secondary support, such as a holder.
What is needed is a means to accomplish processing and analysis after the second lift-out step of attaching the lifted sample to the end-effector of the nanomanipulator without the need for attachment of the sample to a secondary holder.